In addition to skeletal, smooth and cardiac muscle, many animals have an unusual muscle in the beating hearts of the lymphatic system (LHM muscle). Unlike the three main muscle types, the tissue origin and signals that induce LHM cells to form have not been studied and are not known. This project seeks to discover the origin of LHM by labeling potential origin tissues and transplanting them to unlabeled hosts. These studies should reveal the origin of LHM cells and the origin of signals that may induce their formation.